Approaching energy-positive wastewater treatment through production of algal biofuels

Use of photosynthetic microalgae for secondary and tertiary wastewater treatment enables effective BOD and nutrient removal with no energy required for aeration. Algae dewatering via suspended air flotation (SAF) results in two streams: clean effluent suitable for discharge or reuse and concentrated algae slurry suitable for biofuel production. The resulting algae slurry, containing 10-20% solids by weight, can be converted directly to biofuel at high heat and pressure via hydrothermal liquefaction (HTL). The integrated process represents an energy-positive treatment train that couples high effluent quality with production of valuable transportation fuel. A 40,000gpd demonstration plant for this combined technology was constructed in Daphne, AL and operated for 12 months. An overview of this process is provided, alongside data from the first year of plant operations.